INCREASING PRICE competition is forcing chemical companies to reduce capital and operating expenditures, and, of course, do it without compromising their plants reliability and performance. Easier said than done, perhaps, but the New Sampling/Sensor Initiative (NeSSI) for delivering process samples to analyzers can help make it happen.
Since it began about five years ago, NeSSI has driven the move to modularize and miniaturize process sampling systems. Presently operating under the Center for Process Analytical Chemistry (CPAC) at the University of Washington in Seattle, NeSSI started as a group of equipment manufacturers and operating companies.
The group initially sought to build on a standard for modular, surface-mounted systems in the semiconductor industry. It was modified for use in the oil, chemical and petrochemical industries by the SP76 working group of ISAthe Instrumentation, Systems and Automation Society. In 2002, the resulting design became the basis for the international ANSI/ISA-76.00.02 standard for sample flow control, conditioning and analysis. This modular standard basically requires compliant sampling systems to consist of a series of close-coupled, 1.5-in.-square manifolds, each carrying one of the components fastened to the substrate with four hex (Allen wrench) screws.
Saving Sugars Cubes
NeSSIs potential savings were first quantified in 2000 by an ExxonMobil team, which reported that plants switching to NeSSI could save 40% on their sample transport and conditioning system, and eliminate the need for climate-controlled housings. It also projected a 35% savings by reducing sample volumes, as well as carrying and purge fluids, and by requiring less maintenance and support.
After the field experiences with Generation I NeSSI systems, we now have a solid platform to build on, says Jeff Gunnell, lead specialist for process analytics with Scotland-based ExxonMobil Chemical. There has been one round of iteration [in design] since 2001, and these systems work fine in the field within a realistic operating window. ExxonMobil has 30 modular systems installed, including two sites in Baytown, Tex., and one in Sarnia, Ontario, Canada. These systems sample hydrocarbon process streams, and are approaching Best Practice approval status at ExxonMobil. Were considering them for some major projects, and that could mean huge numbers of systems, adds Gunnell.
ExxonMobil adds its modular sampling systems come from two of the three main vendors supplying substrates and other flow components for ANSI/ISA-76.00.02-compliant systems. These are the Instrumentation Division of Parker Hannifin, Swagelok, and Circor Instrumentation Technologies.
|FIGURE 1: UP ON BLOCKS|
In Swageloks MPC system, devices, such as valves, mount on substrate modules containing specialized channel and flow components.
While many of its Generation I modular-sampling are serving well worldwide, NeSSIs Generation II is moving beyond physical fluid handling to integrating the modular systems into plant control hierarchies.
Rob Dubois, another NeSSI member and senior analytical specialist at Dow Chemical, says many modular systems are used in ethylene-hydrocarbon and ethylene oxide production applications and on a continuous-emissions-monitoring system for NOX at his plant in Fort Saskatchewan, Alberta.
"Technically, the NeSSI systems work well and many of the modular components that previously had been missing are now available or are coming to market, he says. However, implementation has been slower than hoped for due to higher costs when compared to conventional systems. Right now, were missing a single-block, combined flow transmitter/indicator, which would really simplify and ease construction. Analyzer systems may have become smart, but the sampling system remains archaic. Today, the industry uses a hodgepodge of analyzer I/O, PLCs, DCSs, databases and proprietary systems.
Generation II systems reportedly will solve this problem with a sensor/actuator manager (SAM) operating system, which will act as the communication channel between DCSs and analytical systems. Higher up, NeSSI systems communicate to the DCS using OPC over TCP/IP Ethernet, while Foundation Fieldbus (FF) is preferred at the field level. The CPAC/NeSSI steering committee incorporated FF into NeSSIs Generation II draft specification in February 2005 because its modular systems need FFs intrinsically safe operating capabilities.
This initiative will help the automation industry adapt the merging class of lab on a chip sensors to a miniature/modular smart manifold, says Mel Koch, CPACs ditector.
Dubois adds that Dows systems are operated on a local level, but once the intrinsically safe NeSSI bus is commonplace and supporting sensors and actuators are available, users will see tighter integration of the sample systems. Some major analytical vendors are now embracing the NeSSI vision, and are adopting both the fluid handling components, as well as the NeSSI-bus/SAM. Actually we have two possible buses: a miniaturized version of FF, which is work in progress, as well as an upcoming version of controller area network bus (CANbus) being undertaken by NIST and IEEEs 1451.6 effort.
Acceptance, Applications Growing
All three companies report theyre making inroads into the process analytical market, and claim doubling sales each quarter. There is a consensus that NeSSI has arrived, says Dave Simko, Swageloks marketing resources manager. Companies using NeSSI systems have shown that the cost savings are real. Although component cost is higher, savings in design time and manufacture generate 30% net savings.
Swageloks Modular Platform Components (MPC) system (See Figure 1 above) consist of fluid-control components, including shut-off, needle, metering, toggle and check valves, and filters, which are mounted on a substrate layer of 1.5-in.-square modules containing specialized channel and flow components.
|FIGURE 2: GO WITH THE FLOW PATH|
|Three-way flow paths required by sampling systems are intrinsically supported by Parker Hannifins Intraflow substrate system.
Parker adds another advantage of Intraflow is its support for the three-way flow paths required for sampling systems, while Swageloks MPC system has sequential flow components that define the flow path. Alternatively, the main flow path in Circors micro Modular Substrate Sampling System (μMS³) is actually external to the Lego-like substrates building blocks, passing through NuBlu tubesets mounted on the blocks.
Despite these gains, Gunnell adds there are limits to NeSSIs methods and technology. Youre not going to get the manufacturers of battleship-sized gas chromatographs (GCs) to change, but a modular sampling system can still sit side-by-side with the analyzer. Where does NeSSI go from here? Generation III systems will doubtless offer added functions, such as Kochs lab on a chip and wireless communications, making them even easier to install and operate.
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